This invention relates to winding apparatus for use in the manufacture of structures of filament-reinforced plastics or filament-reinforced elastomeric material. Typically, but not exclusively, the structure is intended to be used as a pressure vessel, for example by acting as the casing of a solid propellant rocket motor and containing the solid fuel therein. An alternative application of the structure is to provide part of a nozzle assembly for a solid or liquid propellant rocket motor.
Through the last twenty years there have been innumerable designs of winding apparatus aimed at efficiently utilising the tensile strength properties of continuous filament reinforcement materials. Many filament reinforcement materials have been used in such apparatus, examples being glass and carbon. The filament may be used in single strands or in tows of a number of strands lying together and side-by-side to form a ribbon.
Conventional helical winding apparatus usually comprises a mandrel support mechanism which is furnished with a mandrel when it is to be used, and a carriage system bearing a supply of filament. A mandrel drive and the carriage are geared together so that the carriage reciprocates parallel to the mandrel axis as the mandrel is rotated.
In this way filament can be laid on the mandrel in a helical pattern. Longitudinal reinforcement of the wound article can thereby be provided, and this can be strengthened by hoop windings if required.
The invention is particularly concerned with winding of pressure vessels having domed ends, a low length/diameter ratio and a low helix angle. In the type of apparatus disclosed in prior U.S. Pat. No. 3,146,962, in the name of the same inventor, a low helix angle necessitates a substantial movement of the carriage carrying the filament guide beyond the ends of the mandrel. This is undesirable because the machine then occupies a substantial amount of space, and there is a substantial length of filament between the guide and the mandrel at the ends of the carriage traverse. This problem can be mitigated by using a pivotable arm to carry the filament guide, instead of a linearly movable carriage.
In winding certain pressure vessels, in particular rocket motor casings, it is desirable to carefully control the lay of filaments on the mandrel so that the helix angle is substantially constant at a predetermined designed value over the central section of the vessel. The filament guide must then be moved at a constant speed over the central section of the mandrel, but it must move relatively slowly as the filament is laid over the domed ends of the mandrel. However, with low length to diameter ratios, difficulties are encountered in designing a device for pivoting the arm to produce the required velocity characteristic.
The attainment of an accurately controlled helix angle is also facilitated by using a pivotable filament guide as disclosed in the prior United States patent. The present invention provides an elegant solution to the problem of oscillating the arm and the filament guide to give the required lay of filament for the specific type of pressure vessel referred to above.